Healthcare facilities (e.g., nursing homes, hospitals, etc.) typically have a security system to address issues such as patient/resident wandering and infant protection. These systems often operate at low radio frequencies (LF), such as 125 KHz.
FIG. 1 depicts a typical LF security system in hallway 100 of a health care facility. The system includes controller 108, tag 110, and remotely controlled lock mechanism (hereinafter “lock”) 106, the latter element for locking or unlocking doors 104 of doorway 102. As discussed further below, the controller and tag communicate with one another, and, based on those communications and under appropriate conditions, the controller causes the doors to lock.
The salient elements of controller 108, which are depicted in FIG. 2, include processor 212, LF exciter 214, RF receiver 218 (or RF transceiver), and antennas 216 and 220. Elements of tag 110, as relevant here, are depicted in FIG. 3, and include power supply 322, processor 324, data storage 326, LF receiver 328, RF transmitter 330, and antenna 332. Tag 110 is typically worn (e.g., wrist band, ankle band, etc.) by a person, for example, a resident/patient, to control wandering and prevent elopement, or an infant for safety monitoring. See, e.g., “Patient Tag,” “Umbilical Tag,” “Newbaby™ Tag,” commercially available from CenTrak Inc. of Newton, Pa. Tag 110 is typical of a real-time location system (RTLS) tag or security tag, although typically, an RTLS tag includes an RF transceiver (or both an RF transmitter and RF transceiver) while a security tag typically only includes a RF transmitter.
Controller 108 operates as follows. LF exciter 214 transmits, via antenna 216, a low frequency (e.g., 125 KHz) signal. The signal is transmitted at a relatively high-rate of repetition (as frequently as every 100 milliseconds or so, and typically no more than every 500 milliseconds). The packet conveyed by the LF signal includes, among any other information, an identifier (e.g., identification code, etc.) of LF exciter 214. Controller 108 is also capable of receiving an RF signal at its RF receiver 218 via antenna 220. The RF receiver is capable, in conjunction with processor 212, of decoding/extracting information from the received RF signal, and, based thereon, generating and transmitting a control signal (i.e., a “lock command”) to lock 106.
Tag 110 is capable of receiving an LF signal at LF receiver 328 and, in conjunction with processor 324, decoding/extracting information from the signal, such as the I.D. of the LF exciter 214. The tag is further capable, via RF transmitter 330, processor 324, and antenna 332, of generating an RF signal and encoding information therein, such as the I.D. of the LF exciter 212 and the tag's own identifier, the latter retrieved from data storage 326.
Referring now to FIG. 4, which is a protocol flow chart illustrating the operation of the prior-art security system, and with continued reference to FIGS. 1-3, when resident/patient/infant (hereinafter collectively “resident”) R1, wearing tag 110, is in range 109 of LF exciter 214 in controller 108, the tag's LF receiver 328 receives the LF signal transmitted by LF exciter 214. Under the control of processor 324, the LF exciter's I.D. is decoded/extracted from the LF signal. RF transmitter 330 of tag 110 generates an RF signal that encodes the extracted LF exciter I.D. as well as the tag's 110 own I.D. The tag then transmits the RF signal.
RF transceiver 218 in controller 108 receives the RF signal from tag 110 via antenna 220. RF receiver 218 typically operates at a frequency in one of the industrial, scientific, and medical radio bands (“ISM bands”), such as 433 MHz, 902-928 MHz, 2.4 GHz, 5 GHz. The protocol can be a standard protocol, such as Zigbee, Bluetooth, BLE, and WiFi among others, or a proprietary protocol.
RF receiver 218 decodes the received RF signal. If the signal contains the I.D. of LF exciter 212 (indicating, among anything else, that the signal is intended for this particular controller) and optionally the tag I.D., controller 108 sends a lock command to lock 106, thereby locking doors 104, preventing egress of resident R1.
Remotely controlled door locks are widely available and their design and operation is well understood by those skilled in the art and so will only be briefly discussed herein. Such door locks can be controlled via a wired or wireless link. In the illustrative embodiment, controller 108 is hardwired the lock mechanism. To change the state of the lock (i.e., to “lock” it or “unlock” it), controller 108 sends a control signal, which is voltage of some value, to the lock mechanism. In response to the voltage, and via the operation of various relays, switches, actuators, etc., the lock engages or disengages.
The high rate of packet transmission, as noted above, is necessary to make sure that a fast-moving tag (i.e., on a fast-moving person) will receive the LF signal, decode it, and transmit to controller 108 so that a lock command is sent from the controller to lock 106 before the resident arrives at the door.
Security systems employing 125 KHz technology are susceptible to disruption via LF fields emanating from various sources, such as PROX (proximity) card systems. These systems include cards and readers that communicate via 125 KHz RF fields. PROX card systems are often present in healthcare facilities to enable staff to unlock the (same) doors protected by the aforementioned security system. The LF electromagnetic field emanating from the PROX card reader can interfere with the operation of the LF receiver in the tag.
In particular, in the presence of such LF emissions (noise), the tag's LF receiver is not able to recognize the LF signal from the LF exciter or, at least, is not able to recognize the LF exciter's I.D. Although the tag may continue to periodically transmit RF signals in accordance with its normal operation, the signals will not include the LF exciter I.D., since it is not recoverable due to the LF noise. A controller receiving such an RF signal will not transmit a lock command since the LF exciter I.D. is not present (the presence of the LF exciter I.D. in the RF signal triggers the controller to transmit a lock command).
Other equipment, such as cellphone/tablet display screens, and electronic instruments, if placed very close to a tag, can similarly affect a tag based on the LF emissions they generate. This problem is illustrated in FIGS. 5A and 5B, and discussed more fully in the accompanying text.
FIGS. 5A and 5B depict the same environment as FIG. 1, with the same prior-art security system, except that, in FIG. 5A, PROX card reader 540 is now present in hallway 100 to enable a staff member having a PROX card to pass through doorway 102. And in FIG. 5B, resident R1 uses cell phone 544 to circumvent the security system. In particularly, the LF noise emanating from the display of cell phone 544 prevents tag 110 from recovering the LF exciter I.D. As a consequence, the RF signal transmitted by the tag will not include the LF exciter I.D. and, hence, will not trigger a lock command.
Referring to FIG. 5A, resident R1, wearing tag 110, is initially at location L1 beyond the range 109 of signal S1 transmitted from the controller's LF exciter 212. Resident R1 then moves to location L2 within range 109 of the signal, and, consequently, tag 110 receives LF signal S1 from LF exciter 212. The tag then generates and transmits RF signal S2 carrying the I.D. of the LF exciter and its own I.D., as previously discussed. RF signal S2 is received by controller 108. Since the LF exciter I.D. and the tag's I.D are present in RF signal S2, controller 108 sends a “lock command” to lock 106.
Resident R1 continues moving forward towards doorway 102, reaching location L3. This location is within range 542 of LF emissions S3—effectively “noise”—from PROX reader 540. LF emissions S3 interfere with the operation of tag 110, such that any RF signal transmitted by the tag will not contain the LF exciter I.D. (or anything else that would trigger a lock command). Controller 108 receives the RF signal, but the absence of the LF exciter I.D. is interpreted, effectively, to mean that tag 110 has left the immediate area. Consequently, after a predetermined period-of-time elapses since a “lock command” was last received, which is usually about 15 seconds, controller 108 sends an “unlock command” to lock 106. This is depicted in the protocol flow chart of FIG. 4.
It is notable that once tag 110 is in an LF-noise-free environment, it will be able to decode the LF signal from the controller and transmit RF that includes the LF exciter I.D., such that the controller would then issue a lock command. However, in the scenario depicted in FIG. 5A, and as is often the case, PROX card reader 540 is very close to doorway 102, such that the doorway is within range 542 of the LF emissions from PROX card reader 540. As such, resident R1 can reach doorway 102 while tag 110 remains effectively inoperable, pass through the unlocked doors 104, and “escape.”
Turning now to FIG. 5B, resident R1 places cellphone 544 on tag 110 with the intent of circumventing the security system. Initially, the resident is at location L4, which is out of range 109 of the LF exciter in controller 108. Resident R1 eventually moves within range 109, such as to location L5. As a consequence of LF emissions S4 from the display of cell phone 544, the resident's tag 110 cannot process LF signal S1 from the LF exciter. Any RF signals that tag 110 then transmits will not result in controller 108 issuing a lock command (i.e., because the RF signal does not include the LF exciter I.D.).
Assuming that cellphone 544 abuts tag 110 before the resident moves into range 109 of the LF exciter, doors 104 will be unlocked. Assuming cellphone 544 and tag 110 remain very close to one after the resident moves into range 109 of the LF exciter, resident R1 can proceed through doorway 102 without delay (since any RF signal transmitted to the controller would not include the LF exciter I.D.). If cellphone 544 was placed on tag 110 sometime after the resident moves into range 109 of the controller's LF exciter, a lock command would have been issued and the resident might have to wait 15 seconds for the door to unlock. But in either case, someone wishing to defeat the security system is able to do so by exposing tag 110 to LF interference. This same scenario (i.e., placing a cell phone on a tag) can be used by a person wishing to remove a tagged newborn, etc., from such a facility.
FIG. 6 depicts method 600, which shows operations performed by controller 108 of the security system discussed above in conjunction with FIGS. 1-5.
In operation 602, the controller (via its LF exciter) generates and transmits an LF signal. The controller generates the LF signal on a regular basis, such as once every 100 to 500 milliseconds. After generating an LF signal, the controller performs at least some of the operations 603 through 608.
In operation 603, query whether an RF signal is received by the controller (i.e., such as from a tag). If “yes,” then query at operation 604 whether the received RF signal contains the I.D. of the LF exciter and the I.D. of the tag. If “yes,” then at operation 605, cause one or more doors controlled by the controller to lock, such as by sending a “lock command” to the appropriate door(s). Also, a “lock” timer is started.
If the response to the query at operation 604 is “no,” this is interpreted to mean that the RF signal is not from a nearby tag. Query, at operation 606, if the door is locked. If not, processing stops at 609 until the next LF signal is generated at operation 602.
If the response to the query at operation 606 is “yes,” this means that a tag has been in range of the controller recently. Then query, at operation 607, whether the amount of time that the lock timer has been running is greater than or equal to a predetermined value (i.e., “Y” seconds), representing the delay prior to transmitting an unlock command. As previously indicated, a typical value for Y—the delay—is about 15 seconds.
If the query at operation 607 returns a “yes,” then at operation 608, the door is unlocked (i.e., an unlock command is transmitted). Processing then stops at 609 until the next LF signal is generated at operation 602.
If the query at operation 607 returns a “no,” this means that the door should remain locked because an insufficient amount of time has elapsed since the last lock command was received. Processing stops at 609 until the next LF signal is generated at operation 602.
If, at operation 603, the query returns a “no,” this is interpreted to mean that a tag is not in the area. Processing then continues through operations 606 through 608, as appropriate, per the above discussion.
FIG. 7 depicts method 700, which shows operations performed by tag 110 of the security system discussed above in conjunction with FIGS. 1-5.
At operation 702, the tag receives electromagnetic (EM) energy. Query, at operation 703, whether the transmission has a frequency of 125 kHz (or other frequency to which the tag is designed to respond).
If the query at operation 703 returns a “yes,” the I.D. of the LF exciter that generated the LF signal is extracted at operation 704. The tag then generates an RF signal that includes the LF exciter I.D. and the tag's own I.D. at operation 705, and transmits that RF signal at operation 706.
If the query at operation 703 returns a “no,” processing continues at operation 706. The tag continues to send an RF signal, but that signal does not include the LF exciter I.D. As previously discussed, if the EM transmission that the tag receives includes the 125 kHz (LF) signal as well as other LF emissions, the tag will not recognize the LF signal and not decode the Exciter I.D.
As FIGS. 5A, 5B, and 7 illustrate, receiving a “no” in response to the query at operation 604 does not necessarily mean a tag is not in the area. It could be the result of LF noise interfering with the tag's ability to recognize/decode the LF signal from the LF exciter. And in such a situation, prior-art method 600 could result in a door being unlocked when it should remain locked. Consequently, there is a need for a security system, and a method for its operation, that is better able to address the presence of LF noise.